1. Field of the Invention
The present invention relates to a multilayer printed wiring board (PWB) and its manufacturing method and more particularly to a built-up multilayer PWB having a conductive film, which resists peeling, and its manufacturing method.
2. Description of the Related Art
The multilayer printed wiring board is composed of a plurality of layers. Each layer has an insulating film, a via-hole, which is formed in the insulating film and which is plated in its interior, and a conductive film layered on the insulating film. In connection with the conductive layer, there is a so-called voltage plane, which is connected to a signal line and an external power source which transmits current and voltage that are output from the power source to the signal line. The voltage plane is connected to the signal line through plating of the interior of via-hole.
Techniques that relate to the multilayer printed wiring board having the conductive film that is called voltage plane are described in, for example, Unexamined Japanese Patent Publication Nos. S57-149789, S59-161897, and S61-220398.
In these techniques, the conductive film has a plurality of clearances (openings) to prevent occurrence of peeling off the insulating film caused by thermal expansion, etc. The conductive film can disperse stress caused by thermal expansion, etc. to ease by forming the plurality of clearances. The plurality of clearances causes variations in transfer characteristics of the conductive film if the distribution is biased. For this reason, the plurality of clearances is formed in the conductive film to prevent a bias from being generated in the distribution.
In the conventional techniques, the clearances must be designed to prevent contact with the via-hole. However, if the clearances are designed to prevent contact with the via-hole, the distribution of clearances is biased, with the result that variations are generated in the transfer characteristics of conductive film. Further, since the clearances cannot be formed in the vicinity of the via-hole in order to avoid the via-hole, there is a case in which the conductive film close to the via-hole resultantly is peeled off the insulating film by thermal expansion, etc.